24 Proceedings of the Royal Irish Academy. 



In the next series of figures we have the explanation of the apparent 

 discrepancy between the size of the basal disc and that of the thallus which 

 depends on it for resistance to wind action. 



In fig. 9, a longitudinal section of E. calicaris on Sycamore, we have a 

 well-developed specimen of many years' growth. It has one definite main 

 " hapteron " (h), consisting of longitudinally arranged, intertwined hyphae 

 continuous with the similar cortical hyphae (c) rather than with the loose 



ie of the medulla (m) which here ends above the level of the basal disc. 

 From the main hapteron arise lateral blanches of hyphal tissue penetrating 

 the periderm in all directions. 



In sections of older thalli, fig. l<b the medullary tissue extends a sln.ii 



distance below the surface of the periderm, and is seen to merge gradually 



into the more compact cortical tissue. Possibly its appearance below the 



surface level of the periderm is due to the growth of the latter round the 



of the thallus proper. 



In fig. 11 of ];./ on <>ak we have a branched system ( >f haptera 



with islands of periderm tissue and cell-remnants scattered among the 

 hyphae. Hie layers of cork cells are obviously crushed and distorted. The 

 lichen thallus above the periderm gradually merges into a layer of algal cells, 

 fungal hyphae, bark debris, &c, which spreads for some distance over the 

 surface of the stem. 



In fig. 1'J this 1 ■ ially weD developed. Figs. 12 and 1". 



are two of a erse secti-ns taken between a young specimen 



and its parent plant. •:! cm. distant on a twig of Primus spinosa. 

 It will be seen in fig. 12 that though a well-formed hapteron occurs in the 

 outei layers of the peridei he gaps containing smaller hyphal masses 



are most frequent t he bast (J) and cambium [k), even affecting the 



In fig. 14 we have an example of I I of a young Ramalina in the 



spine of a Hawthorn. Considerh . imooth Burface of such a spine, 



it is clearly probable that the younger plants arose from hyphal masses 

 within the periderm, rather than from sporal oi soredial developments on the 



surface. 



t Hi. lichens on tin host plant. 



In fig. 15, representing »n Alder, the centre of the twig 



omposed, and the outer part below the lichen shows Bigns of 



decay. In 16 and 17 we have sections of the edge of the hollow nearest the 



lichen, showing the state of tfa ted tissue and the extension of branched 



and septate hyphae into the open space. It was not found possible to trace any 



